Signs of stress visible in the infrared | Polarjournal

How can we distinguish between calls of recognition and those of distress in a dense penguin breeding colony? The answer lies in the infrared radiation of these animals.

Black heads, large yellow beaks and white plastrons. King penguins grouped in colonies change colour when they are stressed by the passage of a predator, for example. On April 10, the Journal of Thermal Biology published a study showing the usefulness of thermal images for measuring short-term stress among these warm-blooded animals. “Their internal temperature is 38°C thanks to their impermeable plumage, which contributes 80% of the body’s insulation”, explains Agnès Lewden, a scientist specialising on penguins study at the University of Bretagne Occidentale and author of the paper.

To prepare for a possible escape, their blood flow is redirected to the brain and muscles. Their internal body temperature increases, and this can be seen on the surface: the heat of the beak decreases and that of the eye increases. “The eye is a good reflection of what’s going on inside”, explains Antoine Stier, a specialist in penguins studies at the CNRS in Strasbourg, who is also working on the research project.

The camera data comes from 2018-2019. “This is an experiment we carried out in the Baie du Marin in Crozet,” he recalls. The use of thermal cameras avoids the need to take blood samples to assess stress in these animals. This was developed in poultry farming, and biologists then experimented with the method on tits. “We could use infrared photo traps to automate the measurements and develop less invasive tools to measure impacts,” says Antoine Stier.

During their moult, penguins still wear their old feathers as well as their new ones. “They are too thermally insulated,” he explains. Hot, sunny, windless days affect the penguins, which have to evacuate the excess heat. “When it’s hot, we don’t handle them”, explains the researcher. The thermal images can be taken remotely, so the scientists can work on other colonies in the archipelago where the effect of the climate is different, in the Baie de la Chaloupe or the Jardin Japonais.

King penguin colony, Marin Bay, Crozet. Image: Camille Lin

Thermal cameras will also enable biologists to study the phenomenon of habituation to humans. “In the Baie du Marin colony, penguins that are close to a path may be more accustomed to passage than those at the bottom of the colony,” he points out. The cumulative effect of heat waves and human activity such as tourism is becoming increasingly problematic. This was discussed at the 11th International Penguin Congress in Chile last September, with reference to the Humboldt penguin. Other applications could be developed, as infrared colours penguins in other shades, so it’s up to us to interpret the nuances.

Camille Lin, PolarJournal

Link to study: Lewden, A., Ward, C., Noiret, A., Avril, S., Abolivier, L., Gérard, C., Hammer, T.L., Raymond, É., Robin, J.-P., Viblanc, V.A., Bize, P., Stier, A., 2024. Surface temperatures are influenced by handling stress independently of corticosterone levels in wild king penguins (Aptenodytes patagonicus). Journal of Thermal Biology 121, 103850. https://doi.org/10.1016/j.jtherbio.2024.103850.

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